Abstract: SiC nanofibers preforms with different volume fraction of nanofibers were fabricated by the different molding pressures. SiC nanofiber-toughened SiC ceramic matrix composites were prepared by the combined processes of precursor infiltration and pyrolysis with reactive melt infiltration. The effect of molding pressure on the structure and properties of SiC ceramic matrix composites was investigated. Results show that the preforms with high volume fraction of SiC nanofibers can be fabricated by compression molding. When the molding pressure is 40 MPa, the volume fraction of SiC nanofibers is 22.13%. However, there exists the fracture of SiC nanofibers if the molding pressure is too high. The porosity of the composites prepared by the combined processes of precursor infiltration and pyrolysis with reactive melt infiltration is much lower than that by the simple process of precursor infiltration and pyrolysis. The average porosity of the composite materials prepared by these two methods is 1.43% and 14.19%, respectively. When the molding pressure is 30 MPa, the composites have low content of free silicon and the long SiC nanofibers have high length-diameter ratio. Meanwhile, the corresponding value of the bending strength and fracture toughness of the composites is 178 MPa and 21.6 MPa· m^1/2, which is the largest under the different molding pressures.

Key words: SiC nanofiber, molding pressure, precursor infiltration and pyrolysis, reactive melt infiltration, silicon carbide ceramic matrix composite